Differential amplifiers are well known in the art. Such devices typically include an input for receiving an input signal, a reference input for receiving a reference signal, and an output for providing an output signal that is related to a difference comparison between the input signal and the reference signal. With reference to FIG. 3 of the drawings, this output comprises something of an imperfect linear response as depicted in phantom lines by the reference numeral 101.
The applicant herein previously invented a device for more substantially linearizing the above response. With reference to FIG. 1, this previous invention can be seen as depicted generally by the numeral 10. This device (10) included a differential amplifier made up of a first transistor (11), a second transistor (12), and a coupling resistor (13). The base of the first transistor (11) connected to the output of an amplifier (14), the non-inverting input of which connects through a biasing resistor (16) to a reference (17) and also through a coupling capacitor (18) to an input (19) for receiving an input signal. The inverting input of the amplifier (14) connects to the emitter of the first transistor (11) and to a first large current source (21).
The second transistor (12) connects to the output of a second amplifier (22), the noninverting input of which connects to a reference (23) and the inverting input of which connects to the emitter of the second transistor (12) and to a second large current source (24).
So configured, negative feedback will be provided for each transistor (11 and 12), such that the output of the differential amplifier will be substantially linearized. With reference to FIG. 3 again, the linearized output can be seen as represented in solid lines as depicted by the reference numeral 102.
A problem exists, however, with this prior approach of the Applicant. In particular, at the extremes of the operating range of the linearized approach (102), negative feedback current terminates. This, particularly when considered in conjunction with the coupling resistance (13) between the two transistors (11 and 12), leads to instabilities that can create unusual and undesired oscillation modes which can detrimentally impact the performance of the differential amplifier. There therefore exists a need for a means of linearizing a differential amplifier response while simultaneously ensuring stable performance for various input signal amplitudes.